The general mindset is that the ingredients are the most important factor in determining whether a fertilizer can be considered sustainable. While there is no doubt that the ingredients play a major part in the level of sustainability of a given fertilizer, it doesn’t stop there. We must also consider how we use said fertilizer, as well as our method of waste disposal.

It is important to keep in mind that “sustainable” does not necessarily mean the same as “organic” or “natural.” Within the realm of modern growing, sustainability refers to how well the inputs and processes of a grow maintain an adequate level of production to meet demand while preserving the integrity of the environment and protecting consumers. It is driven by a minimalist approach of using only what is needed to reduce waste.

Why Check the Ingredients List of a Fertilizer?

Advocates of organic gardening would say it’s important for a sustainable fertilizer to be made of organic materials. While that’s not necessarily wrong, you must remember that organic isn’t the same as sustainable. When measuring the sustainability of a product, you also must consider the potential toxic trace elements contained in the fertilizer’s ingredients.

Take organic rock phosphate, one of the most ubiquitous sources of phosphate-based fertilizers, for example. This ingredient can contain high levels of arsenic. If not used properly, fertilizers containing it can possibly cause the accumulation of heavy metals. (Read More: The Presence and Transmission of Heavy Metals in Plant Fertilizers). Growers should also be conscientious of their waste management practices to help preserve the environment (more on that below).

On the opposite side of the spectrum, there are plenty of synthetic fertilizers available that are safe and sustainable. When choosing one, avoid fertilizers that include any non-essential plant ingredients such as dyes and perfumes. Plants can’t take up unnecessary ingredients, which tend to end up as waste that is diffused back into the environment as potential contaminants.

Synthetic plant nutrients can be compared to many dietary supplements that people use in addition to the meals they eat throughout the day to achieve proper nutrition. When you use both organic and synthetic fertilizers in gardening, this is referred to as integrated nutrient management. This method, which can take some knowledge and practice to dial in, has the goal of optimizing the plants’ feeding schedule to a level that is most sustainable.

Another buying-point to look for in a sustainable fertilizer is the concentration levels and nutrient ratios of the formula. Blends that are highly concentrated are typically considered more sustainable as they require less water to manufacture. This point only holds true, however, if the nutrient ratios have been methodically calculated by the manufacturer.

These formulas should be 100 per cent water-soluble so plants are able to uptake them without any additional products or potentially locking out selective ions due to inadequate mineral ratios. Multiple-part, crop-specific, and stage-specific formulas (i.e. dutch-style nutrients) have the most potential for higher levels of sustainability due to the points mentioned above.

The Proper Use and Disposal of Fertilizers

No matter if you grow in soil or hydro with organics or synthetics, there is a shared goal of reducing waste and potential environmental contamination. For those growing in a sterile, hydroponics setting, sustainable nutrient management is rather simple. Assuming you have chosen a nutrient regime per the standards above, the next step is knowing what to do with the unused nutrient solution.

One relatively easy, sustainable technique involves running the unused nutrient solution through a reverse osmosis filter. Once the filter becomes saturated with minerals, it can be easily discarded. The filter catches the leftover minerals, leaving the water virtually clear of particles. Once the filter becomes saturated, it can be discarded or taken to a hazardous waste disposal facility.

For those growing in soil, there are a few extra precautions to consider. As touched on before, nutrients and their possibly toxic byproducts can build up in the soil over time. For container gardeners, it is wise to leach (flush) the soil during and at the end of each grow cycle to remove the salt buildup that could cause nutrient imbalances—which could negatively affect the production level of the crop—or toxicity and sacrifice the production level of the crop.

To achieve sustainability while using fertilizer, it is not only important that growers remain conscious of their products’ ingredients, but they must find ways to optimize their production with sustainable techniques that have been tailored to accommodate all of their inputs and unique practices.